Gas filled discharge device



Sept. 26, 1933. F. MEYER Er AL GAS FILLED DISCHARGE DEVICE Filed March28, 1929 2 Sheets-Shget l Wl'fNESS H/i/VS J SPAN/YER QLM/MM Sept. 26,1933. ER r AL 1,928,202

GAS FILLED DISCHARGE DEVICE Filed March 28, 1929 2 Sheets-Sheet 2 J4 7*70 J w J 4 4 7 /d Patented Sept. 26, 1933 i GAS mum DISCHARGE DEVICEFriedrich Meyer and Hans Joachim Spanner, 1 Berlin Halensee, Germany,asslgnora to Eleotrons, Inc., a corporation of Delaware ApplicationMarch 2s, 1929,- Serlal No. 350,778, and in Germany January 27, 1927 25Claims- (Cl. 250-275) This application is a continuation in part of ourbulb is awkward and expensive in construction. application Serial Number214,192 filed 19 August From an operating point of view it isineflicient 1927, and relates to gas-filled discharge devices, becauseof the'long discharge paths physically and particularly to rectifiersoperating with a constricted in cross-sectional area, and further spacecurrent discharge in a gas-filled container electrically so constrictedbecause of the collecwith the aid of an incandescent or heated electrontion of electrical charges on the side walls of these emitting cathode.paths, both of which effects make the overall A particular object of theinvention is to direct drop of potential between cathode and anodes andcontrol the discharges necessary to current high, inconstant anduncontrollable. rectifying actions to prevent improperly timed TheseGermershausen tubes have in them the discharges and discharges betweenthe wrong advantage pointed out by him of substantially electrodes.eliminating the so-called cathode drop or dif- Another object is toconserve in the matter of ference of potential in the cathode darkspace, space needed by the device, and at the same time and thuseliminate this drop from the over-all to provide for eflicientoperation. potential. For example, in an argon atmosphere A furtherobject is to provide an arrangement of about one millimeter of mercurypressure a permitting of rectifying high potential alternat potent aComponent of 8b0uii'130 Volts is elimiing currents without resorting towidely spaced nated, which voltage b d the Cathode dark electrodes andawkward constructions of the conspace is necessary to impart suflicientvelocity to 20 tainer or tube. 1 ions to create suflicient electronemission by A feature of the invention is the use of screens bombardmentfrom a cold electrode when such is between and around electrodes and theuse of used for starting the general ionization of the auxiliaryelectrodes for directing, confining and discharge path. The set ofconditions above cited controlling the rectifying discharges to arriveat for argon are probably the most favorable for the results desired.Another feature is the use easy starting with cold electrodes, so thatwith 80 of the relative effects of an eliminated cathode otherconditions, such as other gases and less drop" at an effective electronemitting cathode favorable cathode materials, the cathode drop is andthe mean free path of electrons in a gaseven higher, and under theseless favorable confilling. Simple and inexpensive construction isditions the beneficial effect of the heated electron v an additionalfeature. emitting cathode is greater. 85

The general operating advantages of gas-filled As pointed out byGermershausen, the other rectifier tubes operating with the aid ofheated drop of potential components of the discharge effective electronemittingcathodes, such as for path are small compared to the cathodedrop. example the well-known oxide coated cathodes of These othercomponents are two. in number and 5 Wehnelt, the German scientist, areably pointed comp se t e d p in the luminous Portion of the 90 out byGermershausen in an article in the June path and the so-called anodedrop, which is and July 1920 issues of Helios, anelectrotechnirepresentative of the potential needed to create calpublication of Leipzig, Germany. However, ionization of the particulargas used, which in the Germershausen and others prior to us, have failedcase of argon is about 12 volts. The drop in the to arrive atsatisfactory simple and inexpensive luminous portion depends upon thelength of the 5 constructions for such rectifying and like disdischargepath, its cross-sectional area, the incharge tubes with provisions fordesirable eftensity of the discharge, the nature of the gas ficiency ofoperation, a fact readily appreciated and the pressure of the gas. Inour practice by examining the tubes of Germershausen illusthis luminousdrop is of the order of a few percent trated in. Fig. 14 of page 258 ofthe June 1920 isof the cathode drop; that is, a few volts. In the 10sues of Helios. The tubes shown in this figure eased the Germershausentubes, Fig. 14 for exare so-called full wave rectifiers. There is ample,the long, constricted and electrically a heated electron emittingcathode in the central charged paths keep this luminous drop high andportion of the bulb co-operating with two anodes inconstant because ofthe inconstancy of the in the ends of the two arms or extensions fromcharges on the walls with intensity of discharge 1 the main portion ofthe bulb, this to get wide sepacurrent. ration between the anodes toconfine the dis- The manner in which our present invention imchargesalternately between the cathode and the proves over the prior art willbe best understood respective anodes, and to avoid breakdown dis-- byreference to the several figures of the draw- (5 charges between theanodes. Obviously, such a ings in which like reference charactersrepresent like parts so far as possible throughout the several figures,andin which Figure 1 is a diagrammatic view of the arrangement ofelectrodes and shields with a gas-filled tube. a

Figure 2 shows in perspective a full-wave alternating current rectifierof the gas-filled heated electron emitting cathode type in whichprovision is made for preventing undesired discharges between the anodesby using fiat anodes shielded from each other by a heated electronemitting cathode.

Figure 3 is a modification of the arrangement of elements as shown inFigure 2.

Figure 4 illustrates in perspective a full-wave rectifier in which ashield is interposed between the anodes so as to separate the tube intoa plurality of electrically independent discharge spaces with a singleemitting cathode so located as to function with both anodes, andincludes auxiliary shielding and discharge control means.

Figure 4a is an elevation in part of the tube shown in Figure 4;

Figure 4b is a sectional plan view on the line 4b-4b of Figure 4a;

Figures 5 and 6 are modifications of the number arrangement and spacingof shields and electrodes of the type of tube shown in Figure 4;

Figure 'l is a fragmentary showing of a full wave rectifier tube inwhich provision is made for shielding the electrodes when such a tube isto be operated at high voltages;

Figure 8 illustrates a multi-phase alternating current rectifier inwhich provision is made by screening for an electrically separate spacefor each phase, and including multiple cathode elements connected inparallel in which there is one principal element for each space.

Figure 9 is a modification of a tube similar to that of Figure 8 whereintwo anodes are utilized and a sectional cathode, each section of whichcooperates with its corresponding anode and shielding devices for thespace current paths within said tube, and

Figure 10 shows a tube having a sectional cathode, a plurality of anodescooperating therewith, shields for the space-current paths within thetube and a shield surrounding the group of electrodes but independent ofthe coating-within the tube performing the functions thereof as.

hereinafter described with reference to Figure .4. Referring to thediagram of Figure 1, it is the substance of our invention to divide thespace ,within a gas-filled envelope 1 containing a cathode 3 and aplurality of anodes 4', 4" into separate space current paths betweeneach anode 4, 4" and the cathode 3 by means of shields 5, 5', 5" so thatin the operation of a. tube of this character the space current willpass along the desired path within the tube and so that there will besubstantially no leakage between the various electrodes whereby losseswithin the tube might occur.

In Fig. 2, there is shown a rectifier tube having the usual glass orlike container 1 provided with the usual stem 2 through which thelead-in electrode wires pass as indicated in accordance with commonpractice. The tube is arranged for fullwave rectification by having aheated electron emitting cathode 3 and two co-operating anodes 4 and 4",the heating current for the cathode being supplied by way of the twoconductors 9 and 10. There is a gas-filling in the tube of low pressure;for instance argon gas at about one millimeter of mercury pressure. Theanodes 4' and 4" are flat and protected relatively to one another andthe cathode by the interposed cathode 3 as shown. The protection is dueto the fact that the interposed cathode and its emitted cloud ofelectrons act as screening or shielding efiects against break-downdischarges between the anodes. A break-down discharge between the twoanodes would require a condition of suflicient positive ionization inthe gas path between them to generally ionize the discharge path. Forexample, considering that phase of the alternating current cycle whenanode 4 is at a maximum positive potential and anode 4" is at a maximumnegative potential, and the potential between the anodes is double thatbetween either anode and the cathode, there is a discharge by generalionization between the cathode and anode 4'. At this time the strongnegative potential of anode 4" is tending to draw to its neighborhoodthe positive ions from the field between the cathode and anode 4, and ifit is successful in drawing suflicient positive ions to its neighborhoodto energize this part of the space then a general break-down dischargewill occur. However, for the positive ions between the cathode and anode4' to reach the neighborhood of anode 4" it is necessary that they passthrough the cloud of electrons continuously emitted by the cathode andthe cathodes field action, and are thus subject to neutralization.Therefore, if the tendency for transferring positive ions is not toostrong for the electron emission of the particular cathode suflicientneutralization takes place to prevent a break-down discharge. Thus insuch an arrangement as that of Fig. 2 there is a limit to the amount ofdischarge current or rectifying action that can be had with a givenemitting cathode.

There also has to be considered the possibility of a reverse action ordischarge between the cathode and the anode that is negative. In thecase of Fig. 2 the cathode is the screen or shield, and the flat anodesare located suificiently close to the cathode that each of the spacingsbetween the cathode and the two anodes is comparable to the mean freepath of the electrons in the particular gas and pressure of it used, aneffect fully explained by W. Crookes as early as about 1905 as pointedout in German Patent 209,969 of November 10, 1908. By reason ofemploying a separation having this mean free path relation the electronflow from the negative anode to the cathode does not create positiveionization, so that there is no general ionization or break-downdischarge at this part of the system.

Fig. 3 modifies the arrangement of Fig. 2 by locating the emittingcathode 3 above the anodes 4 and 4". Since in this arrangement thecathode is removed from its interposed position the anodes are movedcloser together to arrive at the separation distance comparable to themean free path relation to prevent a discharge therebetween. The samerelation pointed out in connection with Fig. 2 as between the cathodeand the two anodes is maintained. With this arrangement it is possiblewith not too high currents and potentials to prevent break-downdischarges between the anodes and between the cathode and non-activeanode for the reasons given in connection with Fig. 2. Obviously thissecond arrangement produces a better exposure of the anode surfaces tothe cathode for better formation of discharge paths between the cathodeby way of the electron field and the alternately operating or activeanodes.

Figs. 4. 4a and 4b are different views of the same full-wave rectifierhaving two anodes 4' and 4" shielded from each other by a screen 5, theemitting cathode comprising the two spiral elements 3' and 3" connectedin series relation and supplied with heating current by way of leads 9and 10, this cathode arrangement being located at the top of the screen.This arrangement thus divides the tube 1 into two general dischargesections or spaces. The screen may be either of conducting material orinsulating material superficially rendered conductive, a simple processfor the latter being the'deposit thereon of the usual mirror ei'lectresulting from getter vapor condensation accompanying the usual clean-upprocess in making such tubes.

The walls of the tube also have a coating of the condensed gettermaterial which may be used as screens to aid in directing andcontrolling the discharge by reason of the field action of electricalcharges collected thereon, and for this reason it is not necessary toextend the space dividing screens to the walls of the tube to completelydivide off the discharge spaces. The charges on the dividing screens andwalls tend to prevent undesired discharges taking place by way of thespaces between internal screens and walls.

There is also shown an auxiliary screen 6 in the space above thecathode, which may or may not be necessary depending upon the size ofthe space, operating voltages and currents and resulting field actions.Its purpose is to prevent positive ions on the active side of the systemfrom escaping in undesired number through this space to the inactiveside. It acts as an auxiliary in this respect to the cloud of electronsabove the oathode. As before stated, it need not span the space entirelyif used, as the charges that collect on it will cooperate with thecharges that collect on the getter surface of the walls of the tube toprevent discharges by way of passages between screen and walls. 7

The screens 5 and 6 are shown connected to the cathode by way ofconnections 8 and 7 re spectively and the getter conducting surface onthe tube walls also so connected by way of crossconnecting element 17between the walls and the screen 5. These connections permit ofcontrolling the degree of electrical charges collecting on theseelements, and therefore the resulting field actions of these charges onthe operating discharges of the tube. Under some operating conditions ofpotential and current it is not necessary to connect the screens to thecathode or any other point of controlled potential, this because thereis an inherent tendency for the positive ions in the operating dischargepaths to neutralize the rapidly collecting negative charges on thescreens originating with the operating electrodes, so that there is anatural tendency for the screens to automatically maintain an averagepotential the same as the potential of the cathode without a conductiveconnection thereto.

The anodes 4' and 4 Fig. 2, located so as to have a gap separation fromthe screen 5 which is comparable to the mean free path of electrons forthe used gas and pressure of it, this to prevent break-down dischargebetween the anode of negative phase in the operating cycle as explainedin connection with Fig. 2.

The operation of the device of Figs. 4, 4a, and 4b is readilyappreciated from the inherent features of it. Considering the twodischarge paths from are, as in the case of the electron emittingcathode to the anodes 4' and 4" of the alternating current cycle whenanode 4' is positive and anode 4" is negative, the potential of thecathode being midway between the anode potentials, it is apparent thatthe cathode drop (at least 130 volts in argon gas of about 1 millimetermercury pressure) is eliminated from the dis charge path between thecathode and positive anode 4' by reason of the electron emittingcathode, or in other words, the resistance in this path is decidedlylowered, the remaining resistance of the luminous portion and the anodedrop being but small compared to the eliminated cathode drop. At thesame time the cathode drop between the non-emitting shield 5 and anode4' is maintained and since the anode drop is the same in both cases,there will be no discharge between anode 4 and screen 5 so long as thedrop oi potential in the luminous section of the discharge path betweencathode and anode does not exceed the sum of the particular cathode dropof screen 5 and the drop of the luminous section between screen 5 andanode 4'; that is, so long as the overall operating potential of thedischarge path does not exceed that potential necessary to give therequired velocity to ions to effectively free electrons from screen 5upon bombardment in such Way that it can act in effect as a cathode.

Considering the discharge path between the cathode and anode 4",temporarily required to be inactive, the screen 5, charged walls of thetube, the cathode and its electron cloud, and screen 6 if used, serve toeifectively prevent positive ions in disturbing quantity from passingfrom the active section to the inactive section of the tube, so thatthere is no break-down ionization in this inactive portion from thissource. Furthermore, anode 4" is spaced. from screen 5 a distance.comparable to the mean free path oi the electrons, and since this isalso a point of strongest field action between screen 5 and anode 4",the electrons from anode 4" concentratedly escape to the screen withoutany effective positive ionization, but merely as a pure electron currentof very small intensity. Thus, when anode 4 is so polarized in theoperation as to be a cathode with respect to cathode 3' 3", theelectrons are drawn off over a short mean free path of electrons and donot move in the main path over a long distance under high potential tostart a reverse discharge to the emitting cathode. It is thus possibleto operate with unusually high voltages without producing break downdischarges.

It is further apparent that the main discharge paths are easilyconstructed to be short and of extensive cross-section with controlleddirecting fields which do not have excessive electrical destructiveeffects, thereby keeping the drop of potential in the luminous waysmall, which means low losses or high efiiciency.

The controlling of the charges on the screens and walls has the furtherbenefit of suppressing tendency to produce auxiliary oscillations, aheretofore difiicult feature to handle in gas-filled tubes.

Fig. 5 illustrates a modification of the tube of Fig. 4, 4a and 4b inthat two screens 5a and 5b are interposed between the anodes 4 and 4",the cathode 3 being placed between the screens. The discharge paths arebowed by the electrons having to pass over the tops of these arrangementoften desirable for high potential operation.

It is sometimes desirable to apply auxiliary respectively, and assuming.that phase I screens, an

binediy cooperate in the open spaces above the screens.

' stantially as in Fig. '7. In

supply transformer of a rectifier system, series resistance 15 and 16being usual in connections of this kind to prevent excessive currentfiows in such an auxiliary part of the system. Secondary winding 14 ofthe supply transformer is shown connected to the filament or cathode 3supply wires in a manner well-known to the art.

With the screens a and 5b so energized by the auxiliary potentialstheions in the discharge paths can be controlledly deviated to increase thelength of the discharge paths and to prevent their entrance into thenon-active sections, where even a small amount of ions not sumcient tostart general ionization would, by reason of the high negative potentialof the inactive anode imparting highvelocity to such ions, causeconsiderable disintegration of the anodes.

Fig. 8 is a modification of the arrangement of Fig. 5 in that thecathode 3 is removed from a position between the screens 5a and 5b to aposition above them, which can be done for lower voltage operation. Thescreens-5a and 5b may or may not have auxiliary potentials asillustrated in Fig. 5 as the particular use and operation of the tubedictates.

Fig. '1 shows an arrangement diiferent from that of Figs. 4, 4a and 4bin that additional screens 5 and 5" are interposed in the paths betweencathode 3 and anodes 4 and 4" respectively, this in order to bend out orlengthen the discharge paths for higher potential operation, and in thisrespect does not diiler materially from the result ob-. tained in Figs.5 and 6. That is, the screens are arranged in such fashion that astraight line drawn from each of the anodes to the cathode cuts ascreen, this as compared to the arrangement in Figs. 4, 4a and 4b inwhich such straight lines do not cut screens.

Fig. 8 shows a tube in which screens 5a, 5b and 5c divide the tube intothree discharge sections for 3-phase current rectification, it beingintended that an anode 4 be located in each one of the sections. In thiscase the cathodes 3a, 3b and 3c are shown so located that there is onecathode section preferably operating with each of the three dischargesections, the cathodes being shown connected in star for heating fromthe 3- phase supply source. Naturally the electron field effects of allthree cathode sections comshielding effect in the Fig. 9 shows anarrangement in which a two section cathode is connected in series forheating, there being one cathode section superimposed over eachdischarge section.

Fig. 10 shows a tube particularly adapted for high voltage operation byhaving an auxiliary conducting screen 11 surrounding the electrodes andinterposed screens which are arranged subthis construction the chargesare prevented from collecting on the walls of the tube. This preventsinterference with operation of the tube by the approach of the hand orconducting objects, and protects operatingv personnel from unpleasantelectrical shocks.

To distinguish our invention from prior practice with respect to gaseousdischarge tubes it is particularly pointed out that our screeningeffects are possible only in connection with an effective electronemitting cathode such as present heated potentials to the screens, whichis provided for in types of cathodes wherein the cathode drop issubstantially eliminated. For example a gaseous discharge tube operatingwith a cold cathode is described in British Patent 237,236 of June 26,1925, and Fig. 1 of this patent shows the two anodes screened from eachother by a cold cathode. As brought out by the patent the rectifyingaction is obtained by reason of an extremely large ratio of surface areaof cathode to anode, such as 300 to l. The rectifying effect istherefore dependent upon the abnormal cathode drop when the small anodeduring its negative phase of the cycle acts as a cathode with regard tothe more positive main cathode, which abnormal drop limits the amount ofreverse positive ionization current. In other words, the amount ofreverse positive ionization current is limited by the ratio of thesurface areas. The cathode does not act as a shield to prevent positiveionization in the nonactive section of the tube. The cathode does serveas a screen to prevent excessive cross-currents between the two anodesin case the potential difference between them is high enough to overcomethe abnormal cathode drop if the oathode were not placed between them.Obviously the anodes could not be located at distances from the coldcathode comparable to the mean free path of electrons of the used gasand pressure of it, as such location would prevent any efficient orderof discharge at any time, thus rendering the device practicallyinoperative for the purpose intended.

In the case of our arrangement the elimination of the cathode drop andthe presence of the electronic cloud about the heated emittingcathode-permits undisturbed operation between the cathode and thepositively charged anode even when the screen connected with the cathodeis located at a distance from the anodes within the mean free path ofthe electrons. At the same 115 time positive ionization in the negativesection is suppressed effectively. Thus the cold screen between theanodes does not act as a cathode at all, but serves only to control theelectrical conduct of the ionization effects by field actions. 1 0Should the screen have any cathode action as in the case of the Britishpatent the efficiency of the arrangement would be eliminated. Generallyspeaking, our screening effects are obtained by field actions andelectronic clouds. Because our 125 rectification action does not dependupon proportioning the areas of cathode to anode we can use anodes oflarge surface, thereby facilitating cooling and reducing disintegration.which latter feature is further bettered by having lower voltage lossesand. thus less destruction by ion acceleration. In fact, our cathodescan be even of lesser surface area than the anodes.

We have pointed out that our anodes are separatedfrom the screens by adistance comparable 135 to the mean free path of the electrons.Obviously a practical construction requires for mechanical reasons aseparation that will not involve short circuits from vibration andexpansion with heating contacts, and an actual separation 140 of onemillimeter at least must be provided for such conditions. Thisseparation translated into terms of mean free paths of the electrons ofthe rare gases usually employed in discharge tubes limits the gaspressures in the tubes to not exceed- 1 'ing 2 to 3 millimeters ofmercury. Heretofore,

ions due to the high cathode drop in such low pressures would toorapidly disintegrate the small anodes. For example British Patent237,236 referred to prescribes a pressure 01' not less than 19millimeters of mercury. With such a pressure in our tube we wouldrequire a mean free path of the order of one-twentieth of a millimeter,which separation would obviously not permit '01 a practicalconstruction.

As an example of a practical application of some of the features of ourinvention we have constructed among others a full-wave rectifier tube ingeneral similar to the arrangements shown in Figs. 4, 4a and 4b whichhas been successfully used commercially to rectify alternating currentof 350 volts between cathode and anode, or 700 volts between the anodes,with a rectified current output of 500 milliamperes. This tube has undersuch operating conditions an internal loss of potential of but about 30volts, thus giving an unusually high efllciency for such a small device.The tube has a height of but 3 inches and a mean diameter of 2 inches.The cathode is a spiral winding about inches long and 1 inch indiameter. The anodes may be flat as shown in Figs. 4 and 4a orcylindrical in form as shown in Figs. 7 and 10, about inches in heightand 3 inches in diameter. The screen between the anodes has an effectivewidth of about 1 inches and a height of about 1 inch. The screen isfitted at the top with auxiliary screens as shown in Fig. 4 extending 1;of an inch on each side. The cathode spiral is of an inch above thescreen. The top of the anode is about of an inch below the top of thescreen. The anodes are spaced from the screen about I; of an inch. Thewalls of the tube have a coating of condensed magnesium getter connectedto the screen by a metallic spring device. The gas pressure is about onemillimeter of mercury of argon gas.

The operation of this practical tube as outlined completely proves theeffectiveness of the screening features of our invention, as the 350volts between the negative anode and the cathode exceeds by almostdouble the necessary ionization potential between cold electrodes inargon of the said gas pressure when not spaced within the mean free pathof electrons.

Having fully described our invention, we claim:

1. A gas-filled discharge device having an electron emitting cathode, aplurality of co-operating anodes, a conductive screen separating saidanodes from each other and intersecting all straight lines which may bedrawn from one to another of said anodes, said cathode being disposed indischarge relation to all of said anodes, and a discharge deflectingscreen in each of the discharge paths between said cathode and theseveral anodes.

2. A gas-filled full-wave alternating current rectifier tube includingan electron emitting cathode, a pair of co-operating anodes, aconductive screen interposed between said anodes, said cathode beinglocated at one edge of said screen, and an additional screen partiallyobstructing the direct paths between saidcathode and each of saidanodes,'said anodes being spaced from said first screen a distancecomparable to the mean free path of electrons in said gas-filling.

3. A gas-filled discharge tube comprising a cathode having a pluralityof sections, a plurality of anodes corresponding in number to saidcathode sections, means shielding each anode from another, a pluralityof shields connected within said tube to said shielding means, andextending between said cathode sections and said anodes whereby straightline discharge between said anodes and their respective cathode sectionsis prevented, a shield within said tube surrounding said electrodes andthe aforementioned shields'and shielding said tube conductivelyconnecting all of said shields.

4. A gas filled discharge device having an electron-emitting. cathode, aplurality of cooperating anodes, a screen intersecting the direct pathsbetween said cathode and each of said anodes for directing the operatingdischarges between said cathode and said anodes, and a shield withinsaid tube and surrounding said cathode and anodes.

' 5. A gas-filled rectifier tube for alternating current including anelectron-emitting cathode, a cooperating anode spaced from said cathodeto provide a positive ionizing gas path therebetween, a conductiveelement spaced from said anode a distance comparable to the mean freepath of the electrons in said gas-filling and connected to said cathode,said element being positioned in substantially non-interfering relationwith the positive ionization of the discharge path in the direction ofcathode and anode, and a shield within said tube and surrounding saidcathode and anode.

6. An electric discharge tube containing a gas, a plurality of anodes, abarrier interposed between said anodes, said barrier being spaced adistance from said anodes comparable to the mean free path distance 01said gas, an emissive cathode interposed between said anodes, andshielding means within and spaced from the walls of said tube andpartially enclosing said cathode and anodes.

7. An electric discharge tube containing a gas,

a plurality of anodes, a barrier interposed between said anodes, saidbarrier being spaced a distance from said anodes comparable to the meanfree path distance of said gas, a thermionic cathode interposed betweensaid anodes, shielding means within and spaced from the walls of saidtube and partially enclosing all of said electrodes, and means withinsaid tube electrically connecting said shield and barrier. 8. Anelectric discharge tube containing a gas, a plurality of anodes mountedon lead wires, a barrier extending between said anodes and between saidlead-in wires, the surface of said barrier extending beyond all edges ofsaid anodes for substantially completely electrically isolating saidanodes from each other, a thermionic cathode between said anodes, and ashield within and spaced from the walls of said tube and surroundingsaid cathode and anodes.

9. A gaseous discharge tube containing a plurality of anodes, a barrierextending between said anodes, the surface of said barrier extendingbeyond all edges of said anodes for substantially completelyelectrically isolating said anodes from each other, an incandesciblecathode between said anodes, extensions on said barrier formingobstructions to straight line electron paths between said cathode andanodes, and a shield within and spaced from the walls of said tube andpartially enclosing said cathode.

10. A space discharge device comprising the combination of an envelope,a gas-filling within said envelope, an electron-emitting cathode, acooperating anode, a conductive element spaced from said anode adistance comparable to the mean free path of the gas, a conductorconnecting said element to the cathode, and a barrier extending betweensaid cathode and anode means, and means within" whereby the normaldischarge path between the said cathode and anode is lengthened.

11. A rectifier comprising an envelope containing a cathode and a pairof anodes, said ,anodes being mounted on opposite sides of the cathode,an ionizable medium in the envelope at a pressure sufiiciently high tosupport a gaseous discharge, and shielding means mounted about thecathode and adapted to be maintained at a fixed potential with respectthereto, a part of said shielding means being closed at one end andproviding a plurality of discharge openings for permitting the dischargebetween said cathode and said anodes.

12. A rectifier comprising an envelope containing an ionizable medium ata pressure sufilciently high to support a gaseous discharge, a pluralityof anodes and a thermionic cathode, said cathode being subject tocontamination by material sputtered from the anode, and means forshielding the cathode from negatively charged anode material and theanode from dislodged disintegration by bombardment, said meanscomprising a hollow metallic member shielding each anode from thedischarge path to the other anode and adapted to be electrically chargedand enclosing the cathode except for a plurality of oppositely disposedrelatively small discharge openings for permitting a discharge betweensaid cathode and anodes.

13. A rectifier comprising an envelope containing an ionizable medium ata pressure sufiiciently high to support a gaseous discharge, a pluralityof anodes and a thermionic cathode, said cathode being subject tocontamination by material sputtered from the anode and means forshielding the cathode from disintegrated anode material and the anodefrom destructive bombardment, said means comprising a hollow metallicmember connected to the cathode and enclosing the latter except for aplurality of small discharge openings, each opening facing itsrespective anode.

14. A space discharge device comprising the combination of an envelope,8. gas filling within said envelope, an electron emissive cathode, apair of anodes and means adapted to be electrically charged placedbetween and shielding said anodes from each other and partiallyenclosing said cathode, said means having openings through which themain discharge current from said cathode is confined respectively tosaid anodes over paths deflected from the straight lines between saidcathode and anodes, said means providing surfaces exposed to thedischarge paths and adapted to reduce contamination of one electrode byanother.

15. A gas filled discharge tube including an electron emissive cathode,a plurality of cooperating anodes, and conductive shielding meansadapted to be electrically charged and disposed about the cathode, andmeans forming an opening toward each of the anodes through which thedischarge from said cathode is restricted and whereby the discharge pathfrom the cathode to each anode is greater than the mean free path ofelectrons in the gas filling, a portion of the shielding means beingspaced from said anodes a distance comparable to the mean free pathdistance, said means providing surfaces exposed to the discharge pathsand adapted to reduce contamination of one electrode by another.

16. A space discharge device comprising the combination of an envelope,a gas filling liberal a conductive member dividing said envelope-into aplurality of discharge compartments, an anode within each of saidcompartments, an electron emissive cathode within said gas filling indischarge relation to each of said anodes, and a conductive screensurrounding said cathode and said discharge compartments, the distanceof the conductive member from said anodes being comparable to the meanfree path of said gas filling.

17. A gas filled discharge tube comprising a thermionic cathode, aplurality of anodes, and means shielding each anode from another andforming a plurality of separate discharge sections between said cathodeand the respective anodes,

said means comprising a conductive shield surrounding the cathode andconnected thereto.

18. A gas filled discharge tube comprising a thermionic cathode, aplurality of anodes, and means for shielding each anode from another andfrom destructive bombardment by positive ions created in the dischargepath between the cathode and another of said anodes, said meansincluding the emissive cathode and shielding means connected to andpartially enclosing said cathode, thereby providing openings whichpermit the development of a low voltage discharge between said cathodeand each of said anodes.

19. A discharge device comprising an envelope containing gas at apressure sufiicient to support a low voltage discharge, a thermioniccathode adapted to eliminate cathode drop, a cooperating anode, andelectrostatic control means extending between said cathode and anode andsubstantially enclosing the discharge path, the said means beingconductive and located to bend the gaseous discharge from a straightline path be tween said cathode and anode.

20. Electrical apparatus comprising the combination of an evacuatedenvelope containing an anode, a thermionic cathode and electrostaticcontrol means adjacent thereto, a charge of inert gas in said envelopeat a pressure sufiicient to sustain a gaseous discharge, said controlmeans being open to the tube atmosphere and comprising metallic surfacesremote from the concentrated discharge path and substantiallysurrounding the entire length of the discharge path, a portion thereofbeing spaced from said anode a distance comparable to the mean free pathof v the gas, and means connecting said control means.

to said cathode for maintaining it at a potential lower than that of theanode.

21. Electrical apparatus comprising the combination of an evacuatedenvelope containing an anode, a thermionic cathode and electrostaticcontrol means adapted to cooperate therewith, a charge of inert gas insaid envelope at a pressure sufiicient to sustain a gaseous discharge,said control means being open to the tube atmosphere and comprising ametallic surface positioned remote from the concentrated discharge pathand substantially surrounding the cathode and anode, said means alsohaving a portion spaced from the anode a distance comparable to the meanfree path of said gas.

22. Electrical apparatus comprising the combination of an evacuatedenvelope containing an anode, a thermionic cathode and an electrostaticcontrol element adjacent thereto, and a charge of inert gas in saidenvelope'at a pressure suflicient to sustain a low voltage discharge,said control element substantially surrounding the anode and cathode andhaving a portion also substantially surrounding the entire length of thedischarge pat the said element being open to the tube atmosphere andbeing positioned in substantially non-interfering relation to the lowvoltage gas discharge but adapted to prevent discharge in the reversedirection.

23. Electrical apparatus comprising the combination of an evacuatedenvelope containing an anode, a thermionic cathode and electrostaticcontrol means adjacent thereto, and a charge of inert gas in saidenvelope at a pressure sufiicient to sustain a gaseous discharge, saidcontrol means being conductive and disposed about the anode and cathodeand having a portion also substantially surrounding the entire length ofthe discharge path, the said means being open to the atmosphere of saidenvelope and adapted to reduce the effects of wall charges on thestarting of the gaseous discharge, said control means being positionedin substantially non-interfering relation to the gaseous dischargebetween the cathode and anode.

24. A gas filled discharge tube containing an electron emissive cathode,a plurality of cooperating anodes, and shielding means between saidanodes and substantially enclosing said cathode, said means adapted tobe electrically charged and providing a discharge opening between thecathode and each of said anodes, said anodes being spaced from thecathode a distance greater than the mean free path of electrons in thegas filling and a portion of said shielding. means being spaced fromsaid anodes a distance comparable to said means free path.

25. A gas-filled discharge tube comprising a thermionic cathode, aplurality of cooperating anodes, and means for deflecting from astraight line path the operating discharge between said cathode and eachof said anodes, and shielding each anode from the discharge path to theother anode, said means being adapted to be maintained at controlledpotentials and forming a shield within said tube partially enclosingsaid cathode.

